In general, a solar cell is one of photovoltaic devices.
A photovoltaic device is a clean energy source for producing energy by converting light energy transferred from the Sun to the Earth into electric energy. A lot of research has been actively conducted into photovoltaic devices for many years.
There is an advantage in that photovoltaic generation using a solar cell or the like can obtain an energy source using new renewable energy anywhere without destroying the environment.
Accordingly, research is being actively conducted into a next generation clean energy source for photovoltaic generation.
At present, the use of a Si single-crystal solar cell widely commercialized for photovoltaic generation is limited due to high manufacturing cost according to use of an expensive wafer.
To address this problem, various attempts have been proposed to develop a thin film solar cell capable of reducing the cost of raw materials and obtaining high efficiency and high reliability.
Among the various attempts, a method for significantly increasing the movement of carriers within a solar cell rather than amorphous Si using a poly-crystal Si thin film formed on a transparent glass substrate is very persuasive.
The aforementioned cell structure has sufficient current conductivity in the Si film itself without using a transparent conducting oxide (TCO) film between the glass substrate and the Si film, thereby remarkably reducing cost as a substitute for a transparent conducting film.
To manufacture poly-crystal Si having excellent properties on the glass substrate below a deformation temperature of glass, low-temperature crystallization of amorphous Si is known as an ideal method.
Among methods for manufacturing low-temperature poly-crystal Si, a method capable of preventing deformation of glass is: (1) an excimer laser annealing (ELA) method using an excimer laser, (2) a metal induced crystallization (MIC) method for inducing crystallization of amorphous Si at a low temperature using metal, and the like.
However, the use of the ELA method in the solar cell is limited due to low uniformity and high manufacturing cost.
In the MIC method as compared with this, specific metal is deposited on an amorphous Si film and then a heat treatment is applied, such that added metal plays a role as a catalyst to progress the Si crystallization. In this method, high uniformity can be achieved at low manufacturing cost.
The MIC method adds metal such as Al, Ni, Co, or the like to the surface of an amorphous Si thin film through sputtering or implantation and performs a heat treatment below a deformation temperature of glass, thereby achieving the Si crystallization.
In particular, when Ni is used, it is known that Si may be crystallized at a relatively low temperature and poly-crystal Si with an excellent crystalline quality may be manufactured.
The poly-crystal Si may be manufactured by moving a NiSi2 phase serving as a combination of Ni and Si in an amorphous Si direction and continuously growing crystalline Si at the rear portion.